It is anticipated that photodynamic therapy (PDT) using PHOTOFRIN at 2.0 mg/kg and a uniform laser light application will reduce the esophageal stricture rate seen and potentially reduce the intensity of the inflammatory reaction without compromising efficacy. The primary objective is to assess the efficacy of PDT with PHOTOFRIN (porfimer sodium) for injection plus omeprazole compared to omeprazole alone in the complete ablation of highgrade dysplasia in patients with Barrett's esophagus, in conjunction with a strict endoscopic surveillance and biopsy protocol. Ablation of HGD should confer a significant clinical benefit to the patient as it eliminates the immediate precursor to invasive cancer and removes the indication for esophagectomy which is associated with mortality and morbidity risks. The secondary objectives are to assess the safety and efficacy of PHOTOFRIN PDT plus omeprazole and systematic endoscopic surveillance compared to omeprazole therapy alone plus systematic endoscopic surveillance in terms of: quality of complete response; duration of complete response; delaying progression to cancer (time to progression); delaying the need for esophagectomy treatment failure; survival.